Tape stiffener, semiconductor device component assemblies including same, and stereolithographic methods for fabricating same

ABSTRACT

Stiffeners for tapes, films, or other connective structures that are configured to be secured to a semiconductor device component, such as a semiconductor die or substrate, by tape-automated bonding processes. The stiffeners are fabricated by stereolithographic processes and may include one or two or more layers. The stiffeners are configured to prevent torsional flexion or bending of the connective structure to which they are to be secured. The stiffeners may reinforce sprocket or indexing holes in connective structures. The stiffeners may include apertures through which intermediate conductive elements or other structures secured to the connective structure may be exposed or protrude. The stereolithographic method for fabricating stiffeners may include use of a machine vision system that recognizes the position and orientation of one or more connective structures on which at least an element of each of the stiffeners is to be fabricated so that the application of material thereto may be controlled.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 09/512,203,filed Feb. 24, 2000, pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to tape structures that are usedin assemblies of semiconductor device components, such as the flexibledielectric tapes that are used in tape automated bonding (TAB) and tapeball grid array (TBGA) packages. Particularly, the tapes of the presentinvention have stiffeners, or support structures, thereon. Morespecifically, the present invention relates to tapes withstereolithographically fabricated stiffeners. The present invention alsorelates to assemblies of semiconductor device components that includethe tapes of the present invention and to stereolithographic methods forfabricating stiffeners on the tapes.

2. State of the Art

TAPES USED WITH SEMICONDUCTOR DEVICE COMPONENTS

In some state of the art semiconductor devices, flexible dielectrictapes with electrical traces thereon are used to connect differentsemiconductor device components. As a first exemplary use of tapes insemiconductor devices, TAB employs flexible dielectric tapes withcircuit traces thereon to electrically connect different semiconductordevice components, such as dice and lead frames or circuit boards. Inanother example of the use of tape in semiconductor devices, a tape withcircuit traces thereon may be used as an interposer in a TBGA package toreroute the outputs of a semiconductor device from the bond padlocations on a semiconductor die with which the tape is assembled todifferent contact pad locations on the tape to which conductive balls orbumps are mounted.

Tapes used in assemblies of semiconductor device components include athin, flexible dielectric film with conductive traces and contact padsformed thereon. Typically, the dielectric films of such tapes are formedfrom polyimide or other suitable polymers. These films are usually onlya few mils (e.g., 6 mils) thick to provide a desired amount offlexibility and to avoid a substantial increase in the overall thicknessof an assembly of semiconductor device components that includes such anelectrically connective tape. The conductive traces and contact pads onsuch films may be formed from a suitable conductive material, such ascopper or aluminum.

Since these tapes are usually flexible, it is sometimes difficult tohold the tape in place to make the desired connections with asemiconductor device component. This is particularly true in TBGApackages, where torsional flexion and bending of the tape areundesirable during bonding of the contact pads of the tape to the bondpads of a semiconductor die. Bending of such tapes is also somewhatundesirable in TAB operations where a row of bond pads, other contactpads, or leads of a semiconductor device component are being bonded toan adjacent row of contact pads on the tape.

In response to these problems, thicker, less flexible tapes have beendeveloped, as have tapes with heavier circuit traces that are positionedto counteract undesirable flexion or bending. Also, tapes that are to beused as interposers in TBGA packages are often supported by a rigidframe, such as a copper or aluminum frame, in order to preventundesirable torsional flexion and bending of the tape during assemblywith, and bonding to, one or more semiconductor dice. When the area ofthe TBGA interposer is relatively large compared to the area of thesemiconductor die, these frames, or stiffeners, may remain in place onthe tape so as to support the portions of the tape that extend laterallybeyond the periphery of the semiconductor die. Stiffeners that remain inplace with respect to the tape following connection of the tape to asemiconductor die are usually electrically isolated from the circuits ofthe TBGA package.

Exemplary TBGA tapes with metal stiffeners and packages including thesame are disclosed in U.S. Pat. No. 6,002,169, issued to Chia et al. onDec. 14, 1999; U.S. Pat. No. 5,844,168, issued to Schueller et al. onDec. 1, 1998; U.S. Pat. No. 5,843,808, issued to Karnezos on Dec. 1,1998; U.S. Pat. No. 5,663,530, issued to Schueller et al. on Sep. 2,1997; U.S. Pat. No. 5,409,865, issued to Kamezos on Apr. 25, 1995; andU.S. Pat. No. 5,397,921, issued to Kamezos on Mar. 14, 1995.

As shown in FIG. 1, in the assembly of a carrier tape 14 to asemiconductor die to form a TBGA package, several TBGA tapes 14 aretypically connected to one another in an elongate strip 10, similar to aroll of photographic film. A semiconductor die is connected on itsactive surface to each TBGA tape 14 of elongate strip 10. Prior toconnecting a semiconductor die to the next, adjacent tape 14, strip 10is moved laterally. Typically, strip 10 includes sprocket or indexingholes 18 near the top and bottom edges 11, 12 thereof to facilitate suchlateral movement. Conventionally, the entire strip 10 of tapes 14 iscarried on a metal (e.g., copper) stiffener or frame 1. Followingconnection of a semiconductor die to a TBGA tape 14, the semiconductordie-TBGA tape assembly, which forms a TBGA package, is severed fromstrip 10.

While conventional metal stiffeners provide support to a tape to be usedin a TBGA package, they only support the tape for purposes of connectionto the semiconductor die and portions of the tape that extend laterallybeyond the periphery of the semiconductor die. Thus, other portions ofthe tape that are prone to flexing or damage during assembly of the tapewith a semiconductor die, such as the sprocket or indexing holes of astrip of TBGA tapes, are not reinforced. Due to the relative thinnessand delicacy of these portions of the tape, however, such reinforcementis desirable.

STEREOLITHOGRAPHY

In the past decade, a manufacturing technique termed“stereolithography”, also known as “layered manufacturing”, has evolvedto a degree where it is employed in many industries.

Essentially, stereolithography as conventionally practiced involvesutilizing a computer to generate a three-dimensional (3-D) mathematicalsimulation or model of an object to be fabricated, such generationusually effected with 3-D computer-aided design (CAD) software. Themodel or simulation is mathematically separated or “sliced” into a largenumber of relatively thin, parallel, usually vertically superimposedlayers, each layer having defined boundaries and other featuresassociated with the model (and thus the actual object to be fabricated)at the level of that layer within the exterior boundaries of the object.A complete assembly or stack of all of the layers defines the entireobject, and surface resolution of the object is, in part, dependent uponthe thickness of the layers.

The mathematical simulation or model is then employed to generate anactual object by building the object, layer by superimposed layer. Awide variety of approaches to stereolithography by different companieshas resulted in techniques for fabrication of objects from both metallicand nonmetallic materials. Regardless of the material employed tofabricate an object, stereolithographic techniques usually involvedisposition of a layer of unconsolidated or unfixed materialcorresponding to each layer within the object boundaries, followed byselective consolidation or fixation of the material to at least apartially consolidated, or semi-solid, state in those areas of a givenlayer corresponding to portions of the object, the consolidated or fixedmaterial also at that time being substantially concurrently bonded to alower layer of the object to be fabricated. The unconsolidated materialemployed to build an object may be supplied in particulate or liquidform, and the material itself may be consolidated or fixed, or aseparate binder material may be employed to bond material particles toone another and to those of a previously formed layer. In someinstances, thin sheets of material may be superimposed to build anobject, each sheet being fixed to a next-lower sheet and unwantedportions of each sheet removed, a stack of such sheets defining thecompleted object. When particulate materials are employed, resolution ofobject surfaces is highly dependent upon particle size, whereas when aliquid is employed, surface resolution is highly dependent upon theminimum surface area of the liquid which can be fixed and the minimumthickness of a layer that can be generated. Of course, in either case,resolution and accuracy of object reproduction from the CAD file is alsodependent upon the ability of the apparatus used to fix the material toprecisely track the mathematical instructions indicating solid areas andboundaries for each layer of material. Toward that end, and dependingupon the layer being fixed, various fixation approaches have beenemployed, including particle bombardment (electron beams), disposing abinder or other fixative (such as by ink-jet printing techniques), orirradiation using heat or specific wavelength ranges.

An early application of stereolithography was to enable rapidfabrication of molds and prototypes of objects from CAD files. Thus,either male or female forms on which mold material might be disposedmight be rapidly generated. Prototypes of objects might be built toverify the accuracy of the CAD file defining the object and to detectany design deficiencies and possible fabrication problems before adesign was committed to large-scale production.

In more recent years, stereolithography has been employed to develop andrefine object designs in relatively inexpensive materials, and has alsobeen used to fabricate small quantities of objects where the cost ofconventional fabrication techniques is prohibitive for same, such as inthe case of plastic objects conventionally formed by injection molding.It is also known to employ stereolithography in the custom fabricationof products generally built in small quantities or where a productdesign is rendered only once. Finally, it has been appreciated in someindustries that stereolithography provides a capability to fabricateproducts, such as those including closed interior chambers or convolutedpassageways, which cannot be fabricated satisfactorily usingconventional manufacturing techniques. It has also been recognized insome industries that a stereolithographic object or component may beformed or built around another, pre-existing object or component tocreate a larger product.

However, to the inventor's knowledge, stereolithography has yet to beapplied to mass production of articles in volumes of thousands ormillions, or employed to produce, augment or enhance products includingother, pre-existing components in large quantities, where minutecomponent sizes are involved, and where extremely high resolution and ahigh degree of reproducibility of results are required. In particular,the inventor is not aware of the use of stereolithography to fabricatestiffeners for tapes that are used to electrically connect semiconductordevices to other semiconductor device components, such as othersemiconductor devices or substrates. Furthermore, conventionalstereolithography apparatus and methods fail to address the difficultiesof precisely locating and orienting a number of pre-existing componentsfor stereolithographic application of material thereto without the useof mechanical alignment techniques or to otherwise assuring precise,repeatable placement of components.

SUMMARY OF THE INVENTION

The present invention includes stiffeners for use on tapes such as TBGAtapes and other tapes that may be suitable for use in TAB applications.The present invention also includes tapes with such stiffeners, as wellas semiconductor devices and assemblies including tapes with suchstiffeners.

The stiffeners of the present invention are preferably fabricated from adielectric material, such as a dielectric photoimageable polymer. Thestiffeners may have any configuration and are preferably shaped toprevent torsional flexion and bending of the tape. For example, astiffener may be located adjacent substantially the periphery of a tape.Alternatively, a stiffener may include one or more elongate, straight ornonlinear elements that traverse the tape. As another alternative, astiffener may include a sheet of material that laterally spreads acrossa portion of the area of the tape. Stiffeners configured as sheets mayinclude apertures through which electrical traces or conductive elementsextend to facilitate electrical connections through the tape.

The stiffeners of the present invention may also be configured toreinforce sprocket or indexing holes through the tape. For example,elongate stiffeners may be located at the top and bottom of a strip oftape, with sprocket or indexing holes being formed therethrough.Alternatively, rings may be formed around individual sprocket orindexing holes or around groups of sprocket or indexing holes toreinforce same.

According to another aspect, the present invention includes a method forfabricating the stiffeners. In a preferred embodiment of the method, acomputer-controlled, 3-D CAD initiated process known as“stereolithography” or “layered manufacturing” is used to fabricate thestiffeners. When stereolithographic processes are employed, eachstiffener is formed as either a single layer or a series ofsuperimposed, contiguous, mutually adhered layers of material.

The stereolithographic method of fabricating the stiffeners of thepresent invention preferably includes the use of a machine vision systemto locate tapes on which the stiffeners are to be fabricated, as well asthe features or other components on or associated with the tapes (e.g.,circuit traces, contact pads, etc.). The use of a machine vision systemdirects the alignment of a stereolithography system with each tape formaterial disposition purposes. Accordingly, the tape need not beprecisely mechanically aligned with any component of thestereolithography system to practice the stereolithographic embodimentof the method of the present invention.

In a preferred embodiment, the stiffeners to be fabricated upon orpositioned upon and secured to a tape or strip of tapes in accordancewith the invention are fabricated using precisely focusedelectromagnetic radiation in the form of an ultraviolet (UV) wavelengthlaser under control of a computer and responsive to input from a machinevision system, such as a pattern recognition system, to fix or cureselected regions of a layer of a liquid photopolymer material disposedon the semiconductor device or other substrate.

Other features and advantages of the present invention will becomeapparent to those of skill in the art through consideration of theensuing description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate exemplary embodiments of theinvention, wherein some dimensions may be exaggerated for the sake ofclarity, and wherein:

FIG. 1 is a top view of a conventional tape strip with metallicstiffeners secured thereto;

FIG. 2 is a top view of an exemplary embodiment of a tape stripincluding a first configuration of stiffeners according to the presentinvention, the stiffeners extending adjacent substantially the entireperipheries of the individual tapes of the strip;

FIG. 2A is a top view of the interlinked stiffeners of the tape shown inFIG. 2;

FIG. 3 is a top view schematic representation of an embodiment of astrip of tape including a second configuration of stiffener reinforcingthe sprocket or indexing holes of the strip;

FIG. 4 is a top view schematic representation of a strip of tapeincluding a third configuration of stiffener reinforcing the sprocket orindexing holes of the strip;

FIG. 5 is a top view schematic representation of a fourth configurationof stiffener, which has an X-shape;

FIG. 5A is a top view of a framework of an interlinked plurality ofstiffeners having the configuration illustrated in FIG. 5;

FIG. 6 is a top view schematic representation of a fifth configurationof stiffener, which includes elongate members;

FIG. 7 is a top view schematic representation of a sixth configurationof stiffener, which includes a sheet of material disposed over the tape;

FIG. 8 is a perspective schematic representation of a TBGA packageincluding the ball grid array tape and stiffener depicted in FIG. 2;

FIGS. 8A and 8B are exemplary cross-sectional representations of theTBGA package of FIG. 8, taken along line 8A—8A, and showing the TBGApackages connected to carrier substrates;

FIG. 9 is a perspective schematic representation of another TBGA packageincluding a tape with a stiffener that extends beyond the periphery ofthe die of the TBGA package;

FIG. 10 is a side view schematic representation of the TBGA package ofFIG. 8 connected face-down to a carrier substrate;

FIG. 11 is a schematic representation of an exemplary stereolithographyapparatus that may be employed in the method of the present invention tofabricate the stiffeners of the present invention; and

FIG. 12 is a partial cross-sectional side view of a tape disposed on aplatform of a stereolithographic apparatus for the formation of astiffener on the tape.

DETAILED DESCRIPTION OF THE INVENTION Stiffeners

With reference to FIG. 2, a strip 10 of tapes 14 for use in TBGApackages or other TAB applications is illustrated. Each tape 14, whichmay be a TBGA tape or TAB tape of known configuration, includeselectrically conductive circuit traces 15 (see, e.g., FIG. 6) thereon,some of which lead to contact pads positioned on the opposite side oftape 14. Tape 14 also includes apertures 17 to facilitate the formationof electrical connections therethrough. Sprocket or indexing holes 18are located near the top and bottom edges 11, 12 of strip 10 andconsistently spaced apart from one another along the top and bottomedges 11, 12 of strip 10 so as to facilitate mechanical indexing ofstrip 10.

A stiffener 20 is secured to each tape 14. Each stiffener 20 shown inFIG. 2 extends adjacent the substantial periphery of the correspondingtape 14. Stiffeners 20 are preferably formed from a rigid dielectricmaterial, such as a photocurable polymer, or photopolymer, to preventbending or torsional flexion of tape 14. Preferably, stiffeners 20 onadjacent tapes 14 are physically separate from one another in order topermit at least some bending of strip 10. FIG. 2A illustrates theframework 220 formed by an elongated series of interlinked stiffeners20.

As shown in FIG. 3, stiffeners 20′ according to the present inventionmay also be employed to reinforce sprocket or indexing holes 18 or otherapertures 17 through tape 14. As illustrated, stiffeners 20′ areelongate members positioned adjacent the top and bottom edges 11, 12 ofstrip 10. Stiffeners 20′ include apertures 22′ therethrough, which arealigned with sprocket or indexing holes 18 of each tape 14. Again,stiffeners 20′ are preferably formed from a dielectric material, such asa photopolymer. The dielectric material from which stiffeners 20′ areformed reinforces sprocket or indexing holes 18 during use thereof toeffect the movement of tape 14. Stiffeners 20′ on adjacent tapes 14 maybe physically separate from one another or extend substantiallycontinuously across the top and bottom edges 11, 12 of strip 10.

FIG. 4 illustrates a variation of stiffeners 20″ that reinforce sprocketor indexing holes 18 of tape 14. Stiffeners 20″ are separate rings orborders that surround the peripheries of and reinforce individualsprocket or indexing holes 18.

Turning now to FIG. 5, another configuration of stiffener 20′″ includestwo intersecting members 24 a′″, 24 b′″, each of which diagonallytraverse tape 14. Members 24 a′″ and 24 b′″ intersect at or near thecenter of tape 14, imparting stiffener 20′″ with an X-shape. Members 24a′″ and 24 b′″ are preferably connected at the point where theyintersect to enhance both torsional and bending support for tape 14.FIG. 5A illustrates the framework 220′″ formed by an elongated series ofinterlinked stiffeners 20′″.

Another configuration of a stiffener 120 incorporating teachings of thepresent invention is depicted in FIG. 6. As shown, stiffener 120includes several elongate members 124 a, 124 b. Elongate members 124 aare substantially straight, while elongate members 124 b are bent,curved, or otherwise nonlinear. Elongate members 124 a, 124 b ofstiffener 120 are preferably arranged upon tape 14 so as to preventundesirable torsional flexion or bending of tape 14. When located on thesame side of tape 14 as that to which a semiconductor die is to besecured, the stiffener 120 structure depicted in FIG. 6 may also beemployed to facilitate alignment of the semiconductor die with tape 14.

FIG. 6 also shows an exemplary arrangement of contact pads 16 a, 16 band circuit traces 15 on tape 14. Contact pads 16 a, shown in phantom,are located on the side of tape 14 on which a semiconductor die is to bepositioned, thereby facilitating connection between bond pads of thesemiconductor die and contact pads 16 a, as known in the art (e.g., bywire bonding, thermocompression bonding, solder balls, conductive epoxysegments, etc.). Circuit traces 15, which are also illustrated inphantom, may be at least partially carried by tape 14 on one or bothsurfaces thereof, as well as internally therethrough. Circuit traces 15communicate with contact pads 16 a and with contact pads 16 b, which maybe located on an opposite side of tape 14 from contact pads 16 a and arepositioned so as to facilitate electrical connection of tape 14 and,thus, of a semiconductor die connected to tape 14 to a higher level, orcarrier, substrate. Alternatively, contact pads 16 a and contact pads 16b may be located on the same side of tape 14. Contact pads 16 a and 16 bare collectively referred to herein as contact pads 16.

FIG. 7 illustrates yet another configuration of stiffener 120′, whichincludes a sheet of dielectric material, such as a photopolymer, thatcovers at least a portion of the surface area of tape 14 to therebysupport same. Stiffener 120′, as well as other embodiments of stiffenersincorporating teachings of the present invention, may also include otherapertures 126 a′, 126 b′.

Referring now to FIGS. 8, 8A, and 8B, a TBGA package 30 is illustratedthat includes a semiconductor die 32 and a tape 14 secured to an activesurface 33 of semiconductor die 32. Contact pads 16 b to whichconductive balls or bumps 28 are secured and the corresponding circuittraces 15 carried by tape 14 are electrically connected, as known in theart (e.g., by wire bonds, thermocompression bonds, solder balls,conductive epoxy segments, etc.), by way of contact pads 16 a tocorresponding bond pads 34 on active surface 33 of semiconductor die 32.Stiffener 20, which is secured to an opposite side of tape 14 thansemiconductor die 32, is preferably positioned so as not to impede theplacement of intermediate conductive elements, such as bond wires 29(FIG. 8B), conductive balls 28, or thermocompression bonds (FIG. 8A),between tape 14 and semiconductor die 32. As shown in FIGS. 8A and 8B,intermediate conductive elements, such as the illustrated conductiveballs 28, conductive epoxy segments, or a conductive material-filledepoxy structure, electrically connect TBGA package 30 to a carriersubstrate 40.

Another embodiment of a TBGA package 30′, depicted in FIG. 9, includes asemiconductor die 32 and a tape 14′ having a greater surface area thanthat of an active surface 33 of semiconductor die 32 to which tape 14′is secured. Thus, tape 14′ extends beyond an outer periphery 35 ofsemiconductor die 32. As illustrated, TBGA package 30′ includesconductive structures 28 (e.g., solder bumps) located beyond outerperiphery 35 and, thus, tape 14′ also includes circuit traces 15 (see,e.g., FIG. 6) that extend beyond outer periphery 35 of semiconductor die32 and contact pads 16 (see, e.g., FIG. 6) that are located outsideouter periphery 35. Tape 14′ has secured thereto a stiffener 120″ thatsupports the portions thereof that extend laterally beyond outerperiphery 35. As shown in FIG. 9, stiffener 120″ is located on the sameside of tape 14′ as semiconductor die 32 and does not, therefore, addsignificantly to the overall thickness of TBGA package 30′.Alternatively, stiffener 120″ may be positioned on the opposite side oftape 14′ from semiconductor die 32. A stiffener 120″ that is positionedon the opposite side of tape 14′ from semiconductor die 32 may alsotraverse tape 14′ opposite semiconductor die 32 to provide additionalsupport to TBGA package 30′.

FIG. 10 illustrates an assembly including TBGA package 30 connected inface-down orientation, or flip-chip bonded, to a carrier substrate 40,as known in the art.

While a plurality of stiffeners incorporating teachings of the presentinvention (e.g., stiffeners 20, 20′, 20″, 20′″, 120, 120′, and 120″,which are collectively referred to hereinafter as stiffeners 20) arepreferably substantially simultaneously fabricated on or secured to acollection of tapes 14, such as on a strip 10 of tapes 14, stiffeners 20according to the present invention may also be fabricated on or securedto a collection of individual or connected tapes 14, or to individualtapes 14. Alternatively, stiffeners 20 may be substantiallysimultaneously fabricated on or secured to a collection of more than onetype of tape 14. As another alternative, different types of stiffeners20 may be substantially simultaneously fabricated on different tapes 14.

Stiffeners 20 may be fabricated directly on tapes 14 or fabricatedseparately from tapes 14, then secured thereto as known in the art, suchas by the use of a suitable adhesive.

As indicated previously herein, stiffeners 20 are preferably fabricatedfrom a dielectric photopolymer. Stereolithographic processes arepreferably used to fabricate stiffeners 20. Thus, each stiffener 20 mayinclude a single layer of at least partially cured photopolymer or aplurality of superimposed, contiguous, mutually adhered layers ofphotopolymer.

Stereolithography Apparatus and Methods

FIG. 11 schematically depicts various components, and operation, of anexemplary stereolithography apparatus 80 to facilitate the reader'sunderstanding of the technology employed in implementation of the methodof the present invention, although those of ordinary skill in the artwill understand and appreciate that apparatus of other designs andmanufacture may be employed in practicing the method of the presentinvention. The preferred, basic stereolithography apparatus forimplementation of the method of the present invention, as well asoperation of such apparatus, are described in great detail in UnitedStates Patents assigned to 3D Systems, Inc. of Valencia, Calif., suchpatents including, without limitation, U.S. Pat. Nos. 4,575,330;4,929,402; 4,996,010; 4,999,143; 5,015,424; 5,058,988; 5,059,021;5,059,359; 5,071,337; 5,076,974; 5,096,530; 5,104,592; 5,123,734;5,130,064; 5,133,987; 5,141,680; 5,143,663; 5,164,128; 5,174,931;5,174,943; 5,182,055; 5,182,056; 5,182,715; 5,184,307; 5,192,469;5,192,559; 5,209,878; 5,234,636; 5,236,637; 5,238,639; 5,248,456;5,256,340; 5,258,146; 5,267,013; 5,273,691; 5,321,622; 5,344,298;5,345,391; 5,358,673; 5,447,822; 5,481,470; 5,495,328; 5,501,824;5,554,336; 5,556,590; 5,569,349; 5,569,431; 5,571,471; 5,573,722;5,609,812; 5,609,813; 5,610,824; 5,630,981; 5,637,169; 5,651,934;5,667,820; 5,672,312; 5,676,904; 5,688,464; 5,693,144; 5,695,707;5,711,911; 5,776,409; 5,779,967; 5,814,265; 5,850,239; 5,854,748;5,855,718; 5,855,836; 5,885,511; 5,897,825; 5,902,537; 5,902,538;5,904,889; 5,943,235; and 5,945,058. The disclosure of each of theforegoing patents is hereby incorporated herein by this reference.

With continued reference to FIG. 11 and as noted above, a 3-D CADdrawing of an object to be fabricated in the form of a data file isplaced in the memory of a computer 82 controlling the operation ofapparatus 80 if computer 82 is not a CAD computer in which the originalobject design is effected. In other words, an object design may beeffected in a first computer in an engineering or research facility andthe data files transferred via wide or local area network, tape, disc,CD-ROM, or otherwise as known in the art to computer 82 of apparatus 80for object fabrication.

The data is preferably formatted in an STL (for STereoLithography) file,STL being a standardized format employed by a majority of manufacturersof stereolithography equipment. Fortunately, the format has been adoptedfor use in many solid-modeling CAD programs, so translation from anotherinternal geometric database format is often unnecessary. In an STL file,the boundary surfaces of an object are defined as a mesh ofinterconnected triangles.

Apparatus 80 also includes a reservoir 84 (which may comprise aremovable reservoir interchangeable with others containing differentmaterials) of an unconsolidated material 86 to be employed infabricating the intended object. In the currently preferred embodiment,the unconsolidated material 86 is a liquid, photocurable polymer, or“photopolymer”, that cures in response to light in the UV wavelengthrange. The surface level 88 of unconsolidated material 86 isautomatically maintained at an extremely precise, constant magnitude bydevices known in the art responsive to output of sensors withinapparatus 80 and preferably under control of computer 82. A supportplatform or elevator 90, precisely vertically movable in fine,repeatable increments responsive to control of computer 82, is locatedfor movement downward into and upward out of material 86 in reservoir84.

An object may be fabricated directly on platform 90, or on a substratedisposed on platform 90. When the object is to be fabricated on asubstrate disposed on platform 90, the substrate may be positioned onplatform 90 and secured thereto by way of one or more base supports 122(FIG. 12). Such base supports 122 may be fabricated before orsimultaneously with the stereolithographic fabrication of one or moreobjects on platform 90 or a substrate disposed thereon. These supports122 may support, or prevent lateral movement of, the substrate relativeto a surface 100 of platform 90. Supports 122 may also provide aperfectly horizontal reference plane for fabrication of one or moreobjects thereon, as well as facilitate the removal of a substrate fromplatform 90 following the stereolithographic fabrication of one or moreobjects on the substrate. Moreover, where a so-called “recoater” blade102 is employed to form a layer of material on platform 90 or asubstrate disposed thereon, supports 122 may preclude inadvertentcontact of recoater blade 102, to be described in greater detail below,with surface 100 of platform 90.

Apparatus 80 has a UV wavelength range laser plus associated optics andgalvanometers (collectively identified as laser 92) for controlling thescan of laser beam 96 in the X-Y plane across platform 90. Laser 92 hasassociated therewith a mirror 94 to reflect laser beam 96 downwardly aslaser beam 98 toward surface 100 of platform 90. Laser beam 98 istraversed in a selected pattern in the X-Y plane, that is to say, in aplane parallel to surface 100, by initiation of the galvanometers undercontrol of computer 82 to at least partially cure, by impingementthereon, selected portions of material 86 disposed over surface 100 toat least a partially consolidated (e.g., semisolid) state. The use ofmirror 94 lengthens the path of the laser beam, effectively doublingsame, and provides a more vertical laser beam 98 than would be possibleif the laser 92 itself were mounted directly above platform surface 100,thus enhancing resolution.

Referring now to FIGS. 11 and 12, data from the STL files resident incomputer 82 is manipulated to build an object, such as a stiffener 20,various configurations of which are illustrated in FIGS. 1-10, or basesupports 122, one layer at a time. Accordingly, the data mathematicallyrepresenting one or more of the objects to be fabricated are dividedinto subsets, each subset representing a slice or layer of the object.The division of data is effected by mathematically sectioning the 3-DCAD model into at least one layer, a single layer or a “stack” of suchlayers representing the object. Each slice may be from about 0.0001 toabout 0.0300 inch thick. As mentioned previously, a thinner slicepromotes higher resolution by enabling better reproduction of finevertical surface features of the object or objects to be fabricated.

When one or more base supports 122 are to be stereolithographicallyfabricated, supports 122 may be programmed as a separate STL file fromthe other objects to be fabricated. The primary STL file for the objector objects to be fabricated and the STL file for base support(s) 122 aremerged.

Before fabrication of a first layer for a support 122 or an object to befabricated is commenced, the operational parameters for apparatus 80 areset to adjust the size (diameter if circular) of the laser light beamused to cure material 86. In addition, computer 82 automatically checksand, if necessary, adjusts by means known in the art the surface level88 of material 86 in reservoir 84 to maintain same at an appropriatefocal length for laser beam 98. U.S. Pat. No. 5,174,931, referencedabove and previously incorporated herein by reference, discloses onesuitable level control system. Alternatively, the height of mirror 94may be adjusted responsive to a detected surface level 88 to cause thefocal point of laser beam 98 to be located precisely at the surface ofmaterial 86 at surface level 88 if level 88 is permitted to vary,although this approach is more complex. Platform 90 may then besubmerged in material 86 in reservoir 84 to a depth equal to thethickness of one layer or slice of the object to be formed, and theliquid surface level 88 is readjusted as required to accommodatematerial 86 displaced by submergence of platform 90. Laser 92 is thenactivated so laser beam 98 will scan unconsolidated (e.g., liquid orpowdered) material 86 disposed over surface 100 of platform 90 to atleast partially consolidate (e.g., polymerize to at least a semisolidstate) material 86 at selected locations, defining the boundaries of afirst layer 122A of base support 122 and filling in solid portionsthereof Platform 90 is then lowered by a distance equal to the thicknessof second layer 122B, and laser beam 98 scanned over selected regions ofthe surface of material 86 to define and fill in the second layer whilesimultaneously bonding the second layer to the first. The process maythen be repeated, as often as necessary, layer by layer, until basesupport 122 is completed. Platform 90 is then moved relative to mirror94 to form any additional base supports 122 on platform 90 or asubstrate disposed thereon or to fabricate objects upon platform 90,base support 122, or a substrate, as provided in the control software.The number of layers required to erect support 122 or one or more otherobjects to be formed depends upon the height of the object or objects tobe formed and the desired layer thickness 108, 110. The layers of astereolithographically fabricated structure with a plurality of layersmay have different thicknesses.

If a recoater blade 102 is employed, the process sequence is somewhatdifferent. In this instance, surface 100 of platform 90 is lowered intounconsolidated (e.g., liquid) material 86 below surface level 88 adistance greater than a thickness of a single layer of material 86 to becured, then raised above surface level 88 until platform 90, a substratedisposed thereon, or a structure being formed on platform 90 or asubstrate thereon is precisely one layer's thickness below blade 102.Blade 102 then sweeps horizontally over platform 90 or (to save time) atleast over a portion thereof on which one or more-objects are to befabricated to remove excess material 86 and leave a film of preciselythe desired thickness. Platform 90 is then lowered so that the surfaceof the film and material level 88 are coplanar and the surface of theunconsolidated material 86 is still. Laser 92 is then initiated to scanwith laser beam 98 and define the first layer 130. The process isrepeated, layer by layer, to define each succeeding layer 130 andsimultaneously bond same to the next-lower layer 130 until all of thelayers of the object or objects to be fabricated are completed. A moredetailed discussion of this sequence and apparatus for performing sameis disclosed in U.S. Pat. No. 5,174,931, previously incorporated hereinby reference.

As an alternative to the above approach to preparing a layer of material86 for scanning with laser beam 98, a layer of unconsolidated (e.g.,liquid) material 86 may be formed on surface 100 of support platform 90,on a substrate disposed on platform 90, or on one or more objects beingfabricated by lowering platform 90 to flood material 86 over surface100, over a substrate disposed thereon, or over the highest completedlayer of the object or objects being formed, then raising platform 90and horizontally traversing a so-called “meniscus” blade over platform90 to form a layer of unconsolidated material having the desiredthickness over platform 90, the substrate, or each of the objects beingformed. Laser 92 is then initiated and a laser beam 98 scanned over thelayer of unconsolidated material to define at least the boundaries ofthe solid regions of the next-higher layer of the object or objectsbeing fabricated.

Yet another alternative to layer preparation of unconsolidated (e.g.,liquid) material 86 is to merely lower platform 90 to a depth equal tothat of a layer of material 86 to be scanned, and to then traverse acombination flood bar and meniscus bar assembly horizontally overplatform 90, a substrate disposed on platform 90, or one or more objectsbeing formed to substantially concurrently flood material 86 thereoverand to define a precise layer thickness of material 86 for scanning.

All of the foregoing approaches to liquid material flooding and layerdefinition and apparatus for initiation thereof are known in the art andare not material to practice of the present invention, so no furtherdetails relating thereto will be provided herein.

In practicing the present invention, a commercially availablestereolithography apparatus operating generally in the manner as thatdescribed above with respect to apparatus 80 of FIG. 11 is preferablyemployed, but with further additions and modifications as hereinafterdescribed for practicing the method of the present invention. Forexample and not by way of limitation, the SLA-250/50HR, SLA-5000 andSLA-7000 stereolithography systems, each offered by 3D Systems, Inc., ofValencia, Calif. are suitable for modification. Photopolymers believedto be suitable for use in practicing the present invention includeCibatool SL 5170 and SL 5210 resins for the SLA-250/50HR system,Cibatool SL 5530 resin for the SLA-5000 and 7000 systems, and CibatoolSL 7510 resin for the SLA-7000 system. All of these photopolymers areavailable from Ciba Specialty Chemicals Corporation.

By way of example and not limitation, the layer thickness of material 86to be formed, for purposes of the invention, may be on the order ofabout 0.0001 to 0.0300 inch, with a high degree of uniformity. It shouldbe noted that different material layers may have different heights, soas to form a structure of a precise, intended total height or to providedifferent material thicknesses for different portions of the structure.The size of the laser beam “spot” impinging on the surface of material86 to cure same may be on the order of 0.001 inch to 0.008 inch.Resolution is preferably ±0.0003 inch in the X-Y plane (parallel tosurface 100) over at least a 0.5 inch×0.25 inch field from a centerpoint, permitting a high resolution scan effectively across a 1.0inch×0.5 inch area. Of course, it is desirable to have substantiallythis high a resolution across the entirety of surface 100 of platform 90to be scanned by laser beam 98, such area being termed the “field ofexposure”, such area being substantially coextensive with the visionfield of a machine vision system employed in the apparatus of theinvention as explained in more detail below. The longer and moreeffectively vertical the path of laser beam 96/98, the greater theachievable resolution.

Referring again to FIG. 11, it should be noted that apparatus 80 usefulin the method of the present invention includes a camera 140 which is incommunication with computer 82 and preferably located, as shown, inclose proximity to mirror 94 located above surface 100 of supportplatform 90. Camera 140 may be any one of a number of commerciallyavailable cameras, such as capacitive-coupled discharge (CCD) camerasavailable from a number of vendors. Suitable circuitry as required foradapting the output of camera 140 for use by computer 82 may beincorporated in a board 142 installed in computer 82, which isprogrammed as known in the art to respond to images generated by camera140 and processed by board 142. Camera 140 and board 142 may togethercomprise a so-called “machine vision system” and, specifically, a“pattern recognition system” (PRS), the operation of which will bedescribed briefly below for a better understanding of the presentinvention. Alternatively, a self-contained machine vision systemavailable from a commercial vendor of such equipment may be employed.For example, and without limitation, such systems are available fromCognex Corporation of Natick, Mass. For example, the apparatus of theCognex BGA Inspection Package™ or the SMD Placement Guidance Package™may be adapted to the present invention, although it is believed thatthe MVS-8000™ product family and the Checkpoint® product line, thelatter employed in combination with Cognex PatMax™ software, may beespecially suitable for use in the present invention.

It is noted that a variety of machine vision systems are in existence,examples of which and their various structures and uses are described,without limitation, in U.S. Pat. Nos. 4,526,646; 4,543,659; 4,736,437;4,899,921; 5,059,559; 5,113,565; 5,145,099; 5,238,174; 5,463,227;5,288,698; 5,471,310; 5,506,684; 5,516,023; 5,516,026; and 5,644,245.The disclosure of each of the immediately foregoing patents is herebyincorporated herein by this reference.

Stereolithographic Fabrication of the Stiffeners

In order to facilitate fabrication of one or more stiffeners 20 inaccordance with the method of the present invention with apparatus 80, adata file representative of the size, configuration, thickness andsurface topography of, for example, a particular type and design of tape14 upon which one or more stiffeners 20 are to be mounted is placed inthe memory of computer 82. Also, if is desired that the stiffeners 20 beso positioned on tape 14 taking into consideration features of ahigher-level substrate 40 (see FIG. 10) to which a semiconductor deviceassembly including tape 14 is to be connected, a data filerepresentative of substrate 40 and the features thereof may be placed inmemory.

One or more tapes 14 may be placed on surface 100 of platform 90 forfabrication of stiffeners 20 thereon. If one or more tapes 14 are to beheld on or above support platform 90 by stereolithographically formedbase supports 122, one or more layers of material 86 are sequentiallydisposed on surface 100 and selectively altered by use of laser 92 toform base supports 122.

Camera 140 is then activated to locate the position and orientation ofeach tape 14 upon which stiffeners 20 are to be fabricated. The featuresof each tape 14 are compared with those in the data file residing inmemory, the locational and orientational data for each tape 14 then alsobeing stored in memory. It should be noted that the data filerepresenting the design size, shape and topography for each tape 14 maybe used at this juncture to detect physically defective or damaged tapes14 prior to fabricating stiffeners 20 thereon or before conductingfurther processing or assembly of tapes 14 with other semiconductordevice components. Accordingly, such damaged or defective tapes 14 maybe deleted from the process of fabricating stiffeners 20, from furtherprocessing, or from assembly with other components. It should also benoted that data files for more than one type (size, thickness,configuration, surface topography) of each tape 14 may be placed incomputer memory and computer 82 programmed to recognize not only thelocations and orientations of each tape 14, but also the type of tape 14at each location upon platform 90 so that material 86 may be at leastpartially consolidated by laser beam 98 in the correct pattern and tothe height required to define stiffeners 20 in the appropriate, desiredlocations on each tape 14.

Continuing with reference to FIGS. 11 and 12, the one or more tapes 14on platform 90 may then be submerged partially below the surface level88 of unconsolidated material 86 to a depth greater than the thicknessof a first layer of material 86 to be at least partially consolidated(e.g., cured to at least a semisolid state) to form the lowest layer 130of each stiffener 20 at the appropriate location or locations on eachtape 14 or other substrate, then raised to a depth equal to the layerthickness, surface 88 of material 86 being allowed to become calm.Photopolymers that are useful as material 86 exhibit a desirabledielectric constant, exhibit low shrinkage upon cure, are of sufficient(i.e., semiconductor grade) purity, exhibit good adherence to othersemiconductor device materials, and have a coefficient of thermalexpansion (CTE) similar to the material of tape 14. Preferably, the CTEof material 86 is sufficiently similar to that of tape 14 to preventundue stressing thereof during thermal cycling of a semiconductor deviceincluding tape 14 in testing, subsequent processing, and subsequentnormal operation. Exemplary photopolymers exhibiting these propertiesare believed to include, but are not limited to, the above-referencedresins from Ciba Specialty Chemical Company. One area of particularconcern is determining resin suitability is the substantial absence ofmobile ions, and specifically fluorides.

Laser 92 is then activated and scanned to direct laser beam 98, undercontrol of computer 82, toward specific locations of surface 88 relativeto each tape 14 to effect the aforementioned partial cure of material 86to form a first layer 20A of each stiffener 20. Platform 90 is thenlowered into reservoir 84 and raised a distance equal to the desiredthickness of another layer 20B of each stiffener 20, and laser 92 isactivated to add another layer 20B to each stiffener 20 underconstruction. This sequence continues, layer by layer, until each of thelayers of each stiffener 20 has been completed.

In FIG. 12, the first layer of stiffener 20 is identified by numeral20A, and the second layer is identified by numeral 20B. Likewise, thefirst layer of base support 122 is identified by numeral 122A and thesecond layer thereof is identified by numeral 122B. As illustrated, bothbase support 122 and stiffener 20 have only two layers. Stiffeners 20with any number of layers are, however, within the scope of the presentinvention. The use of a large number of layers may be employed tosubstantially simulate the curvature of a solder ball to be encompassedthereby.

Each layer 20A, 20B of stiffener 20 is preferably built by firstdefining any internal and external object boundaries of that layer withlaser beam 98, then hatching solid areas of stiffener 20 located withinthe object boundaries with laser beam 98. An internal boundary of alayer may comprise aperture, a through-hole, a void, or a recess instiffener 20, for example. If a particular layer includes a boundary ofa void in the object above or below that layer, then laser beam 98 isscanned in a series of closely spaced, parallel vectors so as to developa continuous surface, or skin, with improved strength and resolution.The time it takes to form each layer depends upon the geometry thereof,the surface tension and viscosity of material 86, and the thickness ofthat layer.

Alternatively, stiffeners 20 may each be formed as a partially curedouter skin extending above a surface of tape 14 and forming a dam withinwhich unconsolidated material 86 may be contained. This may beparticularly useful where the stiffeners 20 protrude a relatively highdistance 56 from the surface of tape 14. In this instance, supportplatform 90 may be submerged so that material 86 enters the area withinthe dam, raised above surface level 88, and then laser beam 98 activatedand scanned to at least partially cure material 86 residing within thedam or, alternatively, to merely cure a “skin” comprising the contactsurface, a final cure of the material of the stiffeners 20 beingeffected subsequently by broad-source UV radiation in a chamber, or bythermal cure in an oven. In this manner, stiffeners 20 of extremelyprecise dimensions may be formed of material 86 by apparatus 80 inminimal time.

Once stiffeners 20, or at least the outer skins thereof, have beenfabricated, platform 90 is elevated above surface level 88 of material86 and platform 90 is removed from apparatus 80, along with anysubstrate (e.g., tape 14) disposed thereon and anystereolithographically fabricated structures, such as stiffeners 20.Excess, unconsolidated material 86 (e.g., excess uncured liquid) may bemanually removed from platform 90, from any substrate disposed thereon,and from stiffeners 20. Each tape 14 is removed from platform 90, suchas by cutting the substrate free of base supports 122. Alternatively,base supports 122 may be configured to readily release each tape 14. Asanother alternative, a solvent may be employed to release base supports122 from platform 90. Such release and solvent materials are known inthe art. See, for example, U.S. Pat. No. 5,447,822 referenced above andpreviously incorporated herein by reference.

Stiffeners 20 and tapes 14 may also be cleaned by use of known solventsthat will not substantially degrade, deform, or damage stiffeners 20 ortapes 14 to which stiffeners 20 are secured.

As noted previously, stiffeners 20 may then require postcuring.Stiffeners 20 may have regions of unconsolidated material containedwithin a boundary or skin thereof, or material 86 may be only partiallyconsolidated (e.g., polymerized or cured) and exhibit only a portion(typically 40% to 60%) of its fully consolidated strength. Postcuring tocompletely harden stiffeners 20 may be effected in another apparatusprojecting UV radiation in a continuous manner over stiffeners 20 or bythermal completion of the initial, UV-initiated partial cure.

It should be noted that the height, shape, or placement of eachstiffener 20 on each specific tape 14 may vary, again responsive tooutput of camera 140 or one or more additional cameras 144 or 146, shownin broken lines, detecting the protrusion of unusually high (or low)preplaced solder balls which could affect the desired distance 56 thatstiffeners 20 will protrude from the surface of tape 14. In any case,laser 92 is again activated to at least partially cure material 86residing on each tape 14 to form the layer or layers of each stiffener20.

Although FIGS. 11 and 12 illustrate the stereolithographic fabricationof stiffeners 20 on a substrate, such as a tape 14, stiffeners 20 may befabricated separately from a substrate, then secured to the substrate byknown processes, such as by the use of a suitable adhesive material.

The use of a stereolithographic process as exemplified above tofabricate stiffeners 20 is particularly advantageous since a largenumber of stiffeners 20 may be fabricated in a short period of time, thestiffener height and position are computer controlled to be extremelyprecise, wastage of unconsolidated material 86 is minimal, soldercoverage of passivation materials is avoided, and the stereolithographymethod requires minimal handling of tape 14.

Stereolithography is also an advantageous method of fabricatingstiffeners 20 according to the present invention since stereolithographymay be conducted at substantially ambient temperature, the small spotsize and rapid traverse of laser beam 98 resulting in negligible thermalstress upon tape 14 or on the circuit traces 15 or contact pads 16thereof

The stereolithography fabrication process may also advantageously beconducted at the wafer level or on multiple substrates, savingfabrication time and expense. As the stereolithography method of thepresent invention recognizes specific types of tape 14, variationsbetween individual tapes 14 are accommodated. Accordingly, when thestereolithography method of the present invention is employed,stiffeners 20 may be simultaneously fabricated on different types oftape 14.

While the present invention has been disclosed in terms of certainpreferred embodiments, those of ordinary skill in the art will recognizeand appreciate that the invention is not so limited. Additions,deletions and modifications to the disclosed embodiments may be effectedwithout departing from the scope of the invention as claimed herein.Similarly, features from one embodiment may be combined with those ofanother while remaining within the scope of the invention.

What is claimed is:
 1. A method for fabricating at least onenonconductive stiffener for a connective structure to be used intape-automated bonding, comprising: disposing at least one layer ofsubstantially unconsolidated material over a platform; and at leastpartially consolidating said at least one layer in selected regions toat least partially form a corresponding layer of the at least onenonconductive stiffener.
 2. The method of claim 1, wherein saiddisposing is effected over at least one connective structure.
 3. Themethod of claim 2, wherein said disposing is effected over a pluralityof connective structures.
 4. The method of claim 3, wherein saiddisposing is effected over a strip including said plurality ofconnective structures.
 5. The method of claim 2, wherein said at leastpartially consolidating comprises at least partially consolidatingmaterial located around peripheries of sprocket holes of said at leastone connective structure.
 6. The method of claim 1, wherein saiddisposing said at least one layer of substantially unconsolidatedmaterial comprises disposing at least one layer of substantiallyunconsolidated photopolymer over said platform.
 7. The method of claim6, wherein said at least partially consolidating comprises directing UVradiation onto at least some of said selected regions.
 8. The method ofclaim 1, wherein said disposing and said at least partiallyconsolidating are repeated to form at least two superimposed,contiguous, mutually adhered layers of the at least one nonconductivestiffener.
 9. The method of claim 1, wherein said at least partiallyconsolidating comprises at least partially consolidating peripheries ofsolid regions of said corresponding layer.
 10. The method of claim 1,further comprising further consolidating partially consolidated materialof the at least one nonconductive stiffener.
 11. The method of claim 1,further comprising securing the at least one nonconductive stiffener toat least one connective structure.
 12. The method of claim 11, whereinsaid securing is effected following said disposing and said at leastpartially consolidating.